No abstract

Focused ion beam (FIB) is an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate, atomically thin materials, especially in extended areas beyond the FIB target, has not yet been fully characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. The emission in these three zones have different wavelengths and decay lifetimes. An unexpected bright ring-shaped emission around the milled location has also been revealed by time-resolved PL spectroscopy with high spatial resolution. Our findings open up new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale.

Hafnium(IV) molecular species have gained increasing attention due to their numerous applications ranging from high-resolution nanolithography, heterogeneous catalysis, and electronics to the design of molecule-based building blocks in metal–organic frameworks (MOFs), with applications in gas separation, sorption, luminescence sensing, and interim storage of radioactive waste. Despite great potential, their chemistry is relatively underdeveloped. Here, we use strong chelators (2Z-6Z)-piperidine-2,6-dione (H3pidiox) and 2,3-dihydroxybenzaldehyde oxime (H3dihybo) to synthesize the first ever reported pentanuclear {Hf5/H3pidiox} and hexanuclear {Hf6/H3dihybo} clusters (HfOCs). The {Hf6} clusters adopt unique core structures [Hf6 IV(μ3-O)2(μ-O)3] with a trigonal-prismatic arrangement of the six hafnium atoms and have been characterized via single-crystal X-ray diffraction analysis, UV–vis spectroscopy in the solid state, NMR, fluorescence spectroscopy, and high-resolution mass spectrometry in solution. One-dimensional (1D) and two-dimensional (2D) 1H NMR and mass spectroscopies reveal the exceptional thermodynamic stability of the HfOCs in solution. Interestingly, the conjunction of the oxime group with the catechol resulted in the remarkable reduction of the clusters’ band gap, below 2.51 eV. Another prominent feature is the occurrence of pronounced metalloaromaticity of the triangular {Hf3} metallic component revealed by its NICS zz scan curve calculated by means of density functional theory (DFT). The NICS zz (1) value of −44.6 ppm is considerably higher than the −29.7 ppm found at the same level of theory for the benzene ring. Finally, we investigated the luminescence properties of the clusters where 1 emits light in the violet region despite the lack of fluorescence of the free H3pidiox ligand, whereas the {Hf6} 3 shifts the violet-emitting light of the H3dihybo to lower energy. DFT calculations show that this fluorescence behavior stems from ligand-centered molecular orbital transitions and that HfIV coordination has a modulating effect on the photophysics of these HfOCs. This work not only represents a significant milestone in the construction of stable low-band-gap multinuclear HfIV clusters with unique structural features and metal-centered aromaticity but also reveals the potential of Hf(IV) molecule-based materials with applications in sensing, catalysis, and electronic devices.

Chiral electronic states of molecules, so-called enantiomers, have an intrinsic sense of handedness, or twist, and are the active component in energy efficient display technologies and in new photosynthetic routes to produce pharmaceuticals. Creating chiral states is achieved by manipulating the “twistiness” of the geometric molecular structure. This is a demanding problem in chemistry adding complexity due to the need to precisely control molecular geometry. Here we demonstrate a novel concept which decouples chirality from molecular geometry. Instead, it exploits the hybridisation of a non-chiral molecule with a chiral electromagnetic field, producing a hybrid light matter chiral polariton state. This is achieved by a symmetry-controlled strong chiral-light–matter interaction between an electromagnetic mode of a chiral nanocavity and an achiral molecule, a concept referred to as the electromagnetic-enantiomer. This electromagnetic mechanism simplifies the creation of chiral electronic states since it is far less demanding in terms of molecular design. We have illustrated the concept using an exemplar system relevant to display technology, producing efficient circularly polarised emission from a non-chiral emitter molecule.